Nouns

(n)aide, auxiliarysomeone who acts as assistant

Adjectives

(s)auxiliary, subsidiary, supplemental, supplementaryfunctioning in a supporting capacity“the main library and its auxiliary branches”
(s)accessory, adjunct, ancillary, adjuvant, appurtenant, auxiliaryfurnishing added support“an ancillary pump”, “an adjuvant discipline to forms of mysticism”, “The mind and emotions are auxiliary to each other”